Brain stem glioma (astrocytoma): Astrocytomas in childhood may occur in the brain stem. This slide demonstrates a sagittal section through the brain in a case of brain stem glioma. The pons and midbrain are considerably swollen. There is focal hemorrhage and necrosis (yellow areas). The floor of the fourth ventricle bulges upward toward the cerebellum. Brain stem gliomas may be of low-grade malignancy or high-grade malignancy.